Is It Necessary to “Spike” Insulin Post-workout?
Another concern of the fat-free-post-workout camp is the blunting of the insulin response. The rationale of maximizing the insulin response is to counteract the catabolic nature of the post-trained state, switching the hormonal milieu into an anabolic one, thus speeding recovery. Although this might benefit those who train fasted or semi-fasted, many don’t realize that a pre-exercise meal (and in some cases the mid-exercise meal) is doing more than enough spiking of insulin levels for anticatabolic purposes.
It’s an important objective to not only maximize muscle protein synthesis, but also minimize protein breakdown. However, the latter doesn’t require a massive insulin spike, but rather just a touch beyond basal/resting levels. To illustrate this, Rennie & colleagues found that even during a sustained high blood level of amino acids, no further inhibition of muscle protein breakdown occurred beyond insulin elevation to approximately 15 μU/l,20 which is slightly above normal basal levels of 5-10 μU/l.
To reiterate, the pre-exercise meal can have profound effects on insulin levels that surpass the length of the training bout. Tipton’s team found that as little as 6g essential amino acids + 35g sucrose taken immediately before exercise (45-50 minutes of resistance training) was enough to keep insulin elevated to roughly 4x above fasting levels 1-hour post-exercise.21 It took 2 hours post-exercise for insulin to return to resting levels. A similar insulin response was seen with 20g whey by itself taken immediately preworkout.22 If carbs were added to the pre-training protein, there would be yet a greater insulin response.
As far as solid food goes, Capaldo’s team examined various metabolic effects during a five hour period after ingesting a meal composed of 75g carb (47%), 37g prot (26%), and 17g fat (27%).23 Although this study didn’t examine training effects, this meal would make a nice post-workout meal due to its absolute (and proportional) amounts of protein and carbohydrate. The fat-fearing camp would warn against the meal’s fat content interfering with the insulin response. However, this meal was able to raise insulin 3 times above fasting levels within 30 minutes of consumption. At the 60 minute mark, insulin was 5 times greater than fasting. At the 300 minute mark, insulin levels were still double the fasting level.
Elliot and colleagues compared the effect of fat-free milk, whole milk, and a higher dose of fat-free milk (to match the calories of the whole milk) taken 60 minutes post-resistance exercise.24 Whole milk was superior for increasing net protein balance. Interestingly, the calorie-matched dose of fat free milk containing 14.5g protein, versus 8.0g in the whole milk (an 81% advantage), but still got beaten. The investigators speculated over the possible mechanisms behind the outcome (insulin response, blood flow, subject response differences, fat content improving nitrogen retention), but end up dismissing each one in favor of concluding that further research is necessary to see if extra fat calories ingested with an amino acid source will increase muscle protein synthesis. Lingering questions notwithstanding, post-workout milkfat was the factor that clinched the victory – at least in overnight-fasted subjects.
To put another nail in the coffin of the insulin spiking objective, post-exercise glycogen resynthesis is biphasic.25 Unlike the subsequent “slow” phase which can last several hours, the initial “rapid” phase of glycogenesis lasting 30-60 minutes immediately post-exercise is not dependent upon insulin. Maximizing post-workout hyperinsulinemia may be beneficial for athletes with more than a single exhaustive endurance-containing training bout separated by less than approximately 8 hours, but in all other cases, the benefit in “spiking” insulin is nil.
In line with this theme, interesting research has surfaced in recent years challenging the idea that highly glycemic (and thus insulinemic) carbohydrates taken post-workout are the optimal for recovery. Erith’s team found no difference between post-exercise high- and low-glycemic index (GI) carbohydrate intake on exercise performance the following day.26 In a similar study, Stevenson’s team actually saw better next-day performance in subjects who consumed low-GI post-exercise carbohydrate than those who consumed high-GI post-exercise carbohydrate.27
Is spiking insulin necessary post-workout? Generally not.
-No greater inhibition of muscle protein breakdown has been seen beyond insulin elevation to approximately 15 μU/l, which is slightly above resting/basal levels of 5-10 μU/l.
-In one study, whole milk was superior for increasing net protein balance post-workout, despite the calorie-matched dose of fat free milk containing 81% more protein.
-The initial 30-60 minute “rapid” phase of glycogenesis immediately post-exercise is not dependent upon insulin.
-There’s no need to attempt to spike insulin for recovery purposes since maximal effects are seen at minimal elevations. Simply getting enough total substrate surrounding the training bout suffices, at least within the context of a 24-hour separation between exhaustive training of the same muscles. Multiple depleting endurance-type bouts per day (i.e., < 8 hours between bouts) may be the exception to this rule.
-On a related tangent, it’s been commonly recommended to maximize post-exercise hyperglycemia and hyperinsulinemia by consuming high-GI carbohydrates. However, this strategy has been seen to offer no benefit on next-day performance, and one recent study even saw endurance impairment.